Hashtable and Queue

[Jedhi]

Let say that I have a Hashtable ht = new Hashtable()

 

My hashtable consist of a key and a value. The value is a Queue. Everytime a command is being saved for this key the queue will be increased. Until a command has been executed and it will there after be decreased.

 

Since I can only add a key to the Hashtable once, how do I then solve this problem ?

[Igor Sukhov]

Let say that I have a Hashtable ht = new Hashtable()

 

My hashtable consist of a key and a value. The value is a Queue. Everytime a command is being saved for this key the queue will be increased. Until a command has been executed and it will there after be decreased.

 

Since I can only add a key to the Hashtable once, how do I then solve this problem ?

 

You need is to add condition check in your code - does hashtable already hold the value for the specific command or not. Have a look at the possible implementations of the Add and ExecuteCommand methods:

 

 

private IDictionary _commands = new Hashtable();

void AddCommand(Key key, Command command)
{
  Queue queue = null;  

  // Check - if there is already the queue of commands for the specific key.  
  //  
  if (_commands.Contains(key))
  {
       queue = (Queue)_commands[key];
  }
  else
  {
       queue = new Queue();
  } 

  queue.Enqueue(command);
  _commands[key] = queue;
}

       void ExecuteCommand(Key key)
       {
           Queue queue = null;

           // Check - if there is already the queue of commands for the specific key.  
           //  
           if (_commands.Contains(key))
           {
               queue = (Queue)_commands[key];
           }

           if (null == queue)
           {
               return;
           }
           else
           {
               Command command = (Command)queue.Dequeue();
               command.Execute();
           }
       }

[Jedhi]

Thank you so much. Your help has really been a big help for me. Thank you so much.

[Joe Mamma]

You may want to consider something like this -

namespace KeyedQueuedCommand
{
public abstract class QueuedCommand 
{
KeyedQueue _queue;

public QueuedCommand(KeyedQueue queue)
{
 _queue = queue;
 _queue.Enqueue(this);
}

protected abstract void OnExecute();

public void Execute()
{
 this.OnExecute();
 _queue.Dequeue();
}
}
public class KeyedQueue:Queue
{
static Hashtable _hash;
object _key;
static KeyedQueue()
{
 _hash = new Hashtable();
}

private KeyedQueue(object key)
{
 _key = key;
 _hash[key] = this;
}

static public KeyedQueue GetKeyedQueue(object key)
{
 lock(_hash)
 {
	if (_hash[key] == null)
	 new KeyedQueue(key);
 }
 return _hash[key] as KeyedQueue;
}

public override object Dequeue()
{
 object result = base.Dequeue();
 Console.WriteLine("Object dequeud from Queue {0}\n{1} Object(s) remaining", 
		_key.ToString(), this.Count.ToString());
 if (this.Count == 0)
 {
	_hash.Remove(_key);
	Console.WriteLine("{0} queue removed", _key.ToString());
 }
 return result;
}

public static void Test()
{
 int i = 0;
 foreach(object key in _hash.Keys)
 {
	KeyedQueue q = _hash[key] as KeyedQueue;
	if ( q != null) i += q.Count; 
 }
 Console.WriteLine("Test - {0} commands left to execute", i.ToString()); 
}
}
}

 

example usage:

public class DateCommand: KeyedQueuedCommand.QueuedCommand
{
public DateCommand(KeyedQueuedCommand.KeyedQueue queue):base(queue){}
protected override void OnExecute()
{
	Console.WriteLine("Executed @ {0}", DateTime.Now.ToLongTimeString());
}
}

private void button1_Click(object sender, System.EventArgs e)
{
Random rand = new Random();
ArrayList commandlist = new ArrayList();
for (int i = 0; i < 100; i++)
{
	commandlist.Add(new DateCommand(
		KeyedQueuedCommand.KeyedQueue.GetKeyedQueue(Math.Round(10 * rand.NextDouble()))));		 
}

foreach(KeyedQueuedCommand.QueuedCommand cmd in commandlist)
	cmd.Execute();

KeyedQueuedCommand.KeyedQueue.Test();
}

Edited January 29, 2006 by Joe Mamma